1. Field of the Invention
This invention relates to reinforcing materials for dental restorations. In particular, this invention relates to fibers for reinforcement of dental restorations, wherein the fibers are high modulus hybrids.
2. Brief Discussion of the Prior Art
Fiber-reinforced composites have found increasing use as structural components in dental restorations, and are described, for example, in U.S. Pat. Nos. 4,717,341 and 4,894,012 to Goldberg et al., as well as U.S. Pat. No. 4,107,845 to Lee, Jr. et al. Fiber-reinforced composites generally comprise at least two components, a polymeric matrix and fibers embedded within the matrix. The polymeric matrix may be selected from those known for use in composite dental materials, for example polyamides, polyesters, polyolefins, polyimides, polyacrylates, polyurethanes, vinyl esters or epoxy-based materials. The fibers used to reinforce composite material may comprises glass, carbon, or polymer fibers such as polyaramide and polyethylene, as well as other natural and synthetic fibers.
Fiber reinforced composite materials provide several advantages, most notably increased strength and stiffness. As described in U.S. Pat. Nos. 4,717,341 and 4,894,012 to Goldberg et al., the contents of which are incorporated herein by reference, such fiber-reinforced composite materials are used as structural components in a variety of dental appliances, taking the form of bars, wires, beams, posts, clasps, and laminates for use in traditional bridges, crowns, artificial teeth, dentures, veneers, and the like. They have also been used in connection with orthodontic retainers, bridges, space maintainers, splints, and the like. In these applications, the fibers preferably take the form of long, continuous filaments, although the filaments may be as short as 3 to 4 millimeters. Shorter fibers of uniform or random length might also be employed. Where the composite structures take the form of elongated wires, the fibers are at least partially aligned and oriented along the longitudinal dimensions of the wire. However, depending on the end use of the composite material, the fibers may also be otherwise oriented, including being normal or perpendicular to that dimension.
Current commercial fiber-reinforced composite materials utilize glass or polyethylene fibers in unidirectional, woven, braided, or mat (non-woven) forms. Glass and polyethylene fibers are currently preferred as being more aesthetic than higher modulus materials. However, the tensile moduli of glass and polyethylene fibers are below 175 GPa. Lower tensile modulus correlates with a lower modulus of elasticity, and thus lower stiffness and greater deflection under load. If the deflection of the structural component exceeds the fracture strain of the overlay or veneer material, the cracking of the latter will result. Thus, while current materials are well-suited for their intended purposes, it would be desirable to use reinforcing fiber materials having a higher tensile modulus, while retaining the aesthetic advantages of glass and polyethylene fibers.